(1) Field of the Invention
The present invention relates to a surface-modified wholly aromatic polyamide fiber and a method of producing same. More particularly, the present invention relates to a wholly aromatic polyamide fiber surface-modified with cation-exchanging inorganic fine particles and a specific additive attached to the fine particles and thus useful for fiber-reinforced rubber or synthetic resinous materials, and a method of producing the same.
(2) Description of Related Arts
It is known that wholly aromatic polyamide fibers have an excellent heat-resistance, a superior mechanical strength, a high elastic modulus and satisfactory chemical resistance and electric property, and thus are usable for various composite materials.
The wholly aromatic polyamide fiber, i.e., the aramide fiber, exhibits a superior mechanical strength in a direction parallel to the longitudinal axis of the fiber, but in a direction transverse to the longitudinal axis of the fiber, the aramide fiber is easily fibrillated due to very high degrees of orientation and crystallinity of the aramide polymer molecules in the fiber. Also, due to this high degree of crystallinity, the surface of the aramide fiber exhibits a poor interface bonding to other materials.
Accordingly, to eliminate the above-mentioned disadvantages, various attempts have been made to improve the surface property of the aramide fiber.
For example, Japanese Unexamined Patent Publication (Kokai) No. 62-97967 discloses a method of producing a wholly aromatic polyamide shaped article having an enhanced bonding property to an organic polymeric matrix, comprising the step of treating a surface of the wholly aromatic polyamide shaped article with an aqueous solution of a metal salt of hypochlorous acid.
Also, Japanese Unexamined Patent Publication (Kokai) No. 62-243620 discloses a surface-modified wholly aromatic polyamide shaped article in which a portion of or all of amide radicals located in a surface portion of a wholly aromatic polyamide shaped article comprising recurring units of the general formula: --NH--Ar.sub.1 --CONH--A.sub.2 --CO-- and/or --NH--Ar.sub.3 --CO--, wherein Ar.sub.1, Ar.sub.2, and Ar.sub.3 respectively and independently from each other represent a divalent aromatic group, are replaced at the nitrogen atoms by an aliphatic organic radical having 2 to 10 carbon atoms.
Further, Japanese Unexamined Patent Publication (Kokai) No. 62-243628 discloses a method of producing a surface-modified wholly aromatic polyamide shaped article, characterized by treating a wholly aromatic polyamide shaped article with an alkali metal salt or alkaline earth metal salt of an aromatic or aliphatic hydrocarbon to convert at least a portion of the amide radicals located in the surface portion of the article to a metal salt radical, and to cause the surface portion of the article to swell, and then treating the surface portion of the article with a polyepoxy compound having at least three epoxy radicals per polymer molecule of the polyamide.
The above-mentioned attempts do not always produce a satisfactory surface-property of the resultant wholly aromatic polyamide fiber.
Particularly, when the wholly aromatic polyamide fibers are converted to a paper-like sheet or nonwoven fabric and are used as reinforcing materials for resinous shaped articles, the fibers usually exhibit a poor resistance to organic solvents for matrix resins of the shaped articles, and thus the reinforcing materials are frequently broken in the step in which the reinforcing materials are impregnated with a solution of a resinous material in the organic solvent.
Also, the reinforcing materials made from the wholly aromatic polyamide fibers exhibit a poor bonding to the matrix resin, and therefore, in a resultant fiber-reinforced shaped article, the reinforcing material is easily peeled from the resinous matrix.
Accordingly, there is a strong demand for a new type of wholly aromatic polyamide fibers having not only a high mechanical strength and elastic modulus but also an enhanced bonding property to another resinous matrix, and thus useful as reinforcing materials for various resinous or rubber articles.